1. Field of the Invention
The present invention relates to input and/or output part of general information communication equipments, electro acoustic equipments, measuring instruments, and systems handling an analog acoustic signal. In particular, the present invention relates to a digital transmitter/receiver implemented in digital speech communication systems.
2. Description of the Prior Art
Conventionally, speech communication using a digital communication system employed an analog to digital converter to convert from analog speech signal to digital transmission at transmitting side and this is recovered to analog signal by a digital to analog converter to drive loudspeaker or earphone at receiving side.
FIG. 4 is a block diagram depicting a schematic configuration of a conventional digital communication system handing analog signals. On a transmitting side, reference numeral 11 denotes an analog microphone; reference numeral 12 denotes an A/D converter; and reference numeral 13 denotes a digital communication channel. On the receiving side, reference numeral 14 denotes a D/A converter, and reference numeral 15 denotes a loudspeaker or earphone.
In such a conventional communication system, there has been a problem that the system requires plural components such as A/D converter, D/A converter, and multiple power supplies annexed thereto, and disturbances such as noise, crosstalk, interference or wiretap in analog signal occurs.
An object of the present invention is to provide digital transmitter/receiver capable of eliminating problems said above associated with the foregoing analog signal and directly connecting analog speech and digital communication systems with each other.
To achieve the foregoing object, a digital transmitter/receiver generates acoustic pulses in magnitude corresponding to digit positions of the pulses of a digital signal by means of electro acoustic transducer elements corresponding to respective bits that forms a digital signal employed in a communication channel, and synthesizes the pulses in an acoustic field (cavity). In this manner, an electro acoustic D/A converter is composed. As in a general electronic A/D converter, the foregoing electro acoustic D/A converter is to be as a component of an A/D converter. This electro acoustic A/D converter is composed of a subtractor, a comparator, an integrator, a sampling circuit, a serial/parallel converter, and a device annexed thereto. In this manner, a transmitter/receiver having a function for converting an analog acoustic signal to a digital electric signal is composed.